Setting a threaded fastener such as a threaded pin and collar combination (nut and bolt) to a predetermined torque, and locking it so it does not loosen is an objective of joints which must retain their reliability. There are numerous approaches to this objective, ranging from the use of lock washers to the use of structurally inherent torque limiting and thread drag means in the collar.
A problem with conventional means of this type is that the locking means frequently requires the exertion of force during the torquing operation to overcome its resistance during the setting operation. This frustrates or makes more difficult the attainment of a known axial tensile preload in the torqued-up joint. Ideally, if the nut or collar were free spinning and frictionless, axial preload in the pin or collar (which preload is the clamping force on the joint) would be directly and almost linearly a function of the applied torque. But many locking systems require deflection of material for the locking action, which must be overcome during the torquing operation by some part of the torque force. The confusion of forces makes more difficult the certain attainment of a known axial preload.
An example of such prior devices is the Hi-Lok fastener shown in Wing U.S. Pat. No. 2,940,495, in which an out-of-round portion of the collar is rounded out by the threaded pin to exert a spring-back locking force on the pin. Although this fastener is very effective and enjoys widespread use, still the forces for axial preload and the forces required to overcome the resistance of the locking means are concurrently applied.
Another example is shown in Wing and Schuster U.S. Pat. No. 3,129,630. In this device, known commercially as the Beta Bolt, before installation, a bolt is threaded into an internally threaded collar, and then the collar is dimpled to distort its inside threads at that point. This distorts the thread on both the pin and outer collar. The distortion on the collar thread will provide a running lock against the pin thread. The collar is inserted into a workpiece and the bolt is turned in the collar to form a head. A disadvantage of this type of device is that when the fastener is set, the deformed parts of the two threads are moved away from each other. The only "locking" action is the drag exerted by the deformed collar. This is not a positive lock in the sense of the instant invention, and again the drag must be overcome while setting the fastener.
Another approach is shown in Stencel U.S. Pat. No. 4,260,005. This device is known as the Eddie Bolt. The collar has protrusions that are abutted by the setting tool to apply the torque, and when the desired torque is reached, then in theory the protrusions fail exactly at that time and no longer can transmit any torque. At that same time the tool is proposed to press against and round out the protrusion material, and through it to press the collar against a non-round thread on the pin. This deformation is theorized to lock the collar onto the pin. The problem is again the confusion of the torque and the locking forces. Because the protrusions must perform two functions, confusion can result. Also, the internal deformation of the collar might not occur at a suitably-shaped part of the thread on the pin to assure locking.
It is an object of this invention to overcome the shortcomings of the above devices. In so doing, a purely free-spinning collar can be spun onto a threaded pin, and to a given torque. The collar can then be locked to the pin by using an entirely separate force system. There is no confusion of forces, and each force can separately be determined and provided. Further objects are to provide a method to attain this, and to provide a tool for doing it.